Many search engine services, such as Google and Overture, provide for searching for information that is accessible via the Internet. These search engine services allow users to search for web pages and other Internet-accessible resources that may be of interest to users. After a user submits a search request that includes search terms, the search engine service identifies web pages that may be related to those search terms. To quickly identify related web pages, the search engine services may maintain a mapping of keywords to web pages. This mapping may be generated by “crawling” the web (i.e., the World Wide Web) to identify the keywords of each web page. To crawl the web, a search engine service may use a list of root web pages to identify all web pages that are accessible through those root web pages. The keywords of any particular web page can be identified using various well-known information retrieval techniques, such as identifying the words of a headline, the words supplied in the metadata of the web page, the words that are highlighted, and so on. Some search engine services can even search information sources that are not accessible via the Internet. For example, a book publisher may make the content of its books available to a search engine service. The search engine may generate a mapping between the keywords and books. When a search engine service receives a search request that includes one or more search terms, it uses its mapping to identify those information sources (e.g., web pages or books) whose keywords most closely match the search terms. The collection of information sources that most closely matches the search terms is referred to as the “search result.” The search engine service then ranks the information sources of the search result based on the closeness of each match, web page popularity (e.g., Google's page ranking), and so on. The search engine service then displays to the user links to those information sources in an order that is based on their rankings.
Some search engine services do not charge a fee to the providers of web pages for including links to their web pages in search results. Rather, the search engine services obtain revenue by placing advertisements along with search results. These paid-for advertisements are commonly referred to as “sponsored links,” “sponsored matches,” or “paid-for search results.” An advertiser who wants to place an advertisement for an item along with certain search results provides a search engine service with an advertisement and search terms. When a search request is received, the search engine service identifies the advertisements whose search terms most closely match those of the search request. The search engine services can either charge for placement of each advertisement along with search results (i.e., cost per impression) or charge only when a user actually selects a link associated with an advertisement (i.e., cost per click).
Advertisers would like to maximize the effectiveness of advertising dollars used to pay for advertisements placed along with search results. Those advertisers try to identify search terms for items being advertised that result in the highest benefit (e.g., most profit) to the advertiser. It would be desirable to have techniques that would allow advertisers to maximize the effectiveness of their advertising dollars by identifying search terms that are more targeted to or related to the item being advertised.